Circuit arrangement supervising tracks of railroads with electric traction



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P. E 2,966,581 CIRCUIT ARRANGEMENT SUPERVISING TRACKS 0F RAILROADS WITH ELECTRIC TRACTION Filed. Dec. 13, 1951 JIGNAL cueeEA/r f5 w) 7', T2 T3 2 Ie I1 6 6 l I l l m In 1 LA [e t5 F/G. Z

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I L m I ,4 TTOE/VEY CIRCUIT ARRANGEMENT SUPERVISING TRACKS OF RAILROADS WITH ELECTRIC TRACTION Friedrich P. Ehni, Stuttgart, Germany, assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Dec. 13, 1951, Ser. No. 261,442 Claims priority, application Germany Dec. 15, 1950 3 Claims. (Cl. 246-35) Track circuits in rail transportation safety systems operate safely only if the track relay checking the occupied and free conditions of an insulated track section is held free from interfering voltages. Such interfering voltages can be set up by stray currents in the track, in particular by power return currents in railroads with electric traction, which affect the track relay. With track sections where both rails are insulated interfering voltages are not usually encountered as a rule, due to the balancing action of impedance bonded joints, while with the simpler and thus less expensive insulated track sections on singlerail basis, in particular with long sectional lengths, they can be very great even in routine operation. The shown drawbacks with such track circuits are eliminated in accordance with the invention by the device that switching means are provided which are controlled by the power return current and thereby cancel the effects of interfering voltages to the track relay.

The invention is preferably so laid out that the power return current sets up in a transformer (T3) such a voltage that the interfering voltage across the relay transformer (T2) is so set off that the relay is not affected by the interference.

A more thorough understanding of the invention may be had from the following detailed description and the accompanying drawing in which:

Fig. 1 is a schematic diagram of the circuit arrangement utilizing the invention; and

Fig. 2 is a schematic diagram of a modification of the circuit shown in Fig. 1.

An insulated track section may comprise the insulated rail i with insulating joints A and B at either end, as well as the grounded rail e. At the one end of the insulated section, the source S connects across the insulated rail and the grounded rail, by way of the transformer T1 having windings 1 and 2. At the other end of the insulating section, this track-clear voltage is fed to the track relay R through the windings 4 and 3 of the transformer T2. The power return current I which flows in the grounded rail e1 in the shown direction of the arrow, divides itself in accordance with the relative impedances in the insulated section in the component Ie in the grounded rail e, and the component Ii in the insulated rail i. The current Ii flows through winding 4 of the transformer T2, so it causes an interfering voltage across the transformer winding 3. At the insulating joint C, the power return current I is led through winding 6 of transformer T3, to generate in its winding a voltage equalling the one set up by Ii by way of the windings 4-3 of transformer T2. By a suitable series connection, such as the opposed secondaries, of the windings 3-4 of transformer T2 and 5-6 of transformer T3, the voltages induced by Ii in transformer T2, and by I in transformer T3 cancel, so they have no effect on relay R, while the track-clear indicating voltage between the insulating rail i and the grounded rail e reaches the relay.

Another embodiment which avoids the insulating joint 1 ted States Patent C of Fig. 1 required in the grounded rail, will be described with the aid of Fig. 2. Here only the relay portion of the circuit with the insulating joint B is shown, as the control input portion with the transformer T1 and the insulating joint A remain the same. The transformer T2 is connected as in Fig. l, and the partial current Ii flows through it. The transformer T3 is connected with its prmiary winding 6 across two spaced points of the grounded rail e. The greatest part of the power return current I, i.e. Ie which flows through this rail section, sets up the voltage Ue across the transformer because of the relatively high impedance of the rail. This is transferred to winding 5 of the transformer T3 in such a transmission ratio that it corresponds to the voltage set up by Ii in winding 3 of transformer T2, so it balances out the latter because of its opposing direction. The voltage sum of the two windings is fed to the track relay R, as before.

To provide concellation of the interfering voltage across the track relay even if the two interfering voltages appearing across the transformers are not in phase, a phase shifting network may be inserted for phase shifting one of the two voltages and the relay.

What is claimed is:

l. A signalling system for electric railways in which the track rails are employed as a return path for traction power currents, and in which one of said rails is insulated and divided into signal sections and the other rail serves as a ground return for the traction current and the signals, the combination for transmitting signal currents and for isolating the effects of said return traction currents from the signaling equipment, comprising the combination of a source of signalling potential applied across said rails, a signalling device coupled across said rails a pair of transformers each having a primary winding and a secondary winding, said primary and secondary windings, respectively, being connected in series, the primary winding of a first of said transformers connected between said one and said other rail, the primary winding of the second of said transformers bridged across a portion of said other rail, the secondary windings of said transformers serially connected with said signal device, said transformer windings being connected to induce substantially equal and opposite voltages in said secondary windings under control of said return traction currents.

2. A signalling system as claimed in claim 1, further comprising means for insulating from one another the portions of said other rail bridged by the primary winding of said second transformer.

3. A signalling system as claimed in claim 1, wherein the portion of said other rail bridged by the primary winding of said second transformer is a continuous track rail.

References Cited in the file of this patent UNITED STATES PATENTS 804,176 Townsend Nov. 7, 1905 1,097,197 Thullen May 19, 1914 1,109,880 Thullen Sept. 8, 1914 1,130,353 Townsend Mar. 2, 1915 1,190,247 Wagner ..July 4, 1916 1,324,152 Holliday Dec. 9, 1919 1,396,888 Scott Nov. 15, 1921 1,770,705 Lucas July 15, 1930 2,098,833 Peter Nov. 9, 1937 2,156,710 Thompson May 2, 1939 FOREIGN PATENTS 424,674 France Mar. 20, 1911 

